Hotpoint Ultima WMD940 what is my problem and how to fix it?

My Hotpoint Ultima WMD940 has electric power to it
screen display okay. I can select program and it appears to start then it stops, timer counts down and after a few minutes error "no water check water supply". Water supply is okay so turned electric supply off at mains for a few minutes switch on again and away it goes no problem. We have been lucky to just do this on a few occasions but it now wont restart at all. Any advice on what problem is and if a fix is possible would be really appreciated. I look forward to any responses.